A hand-held dispensing device for intermixing dental impression materials and for dispensing the mixed product through a common spout is shown and described in U.S. Pat. No. 4,753,536 and 4,538,920, respectively. In general, the prior art dispensing devices broadly consist of a syringe having a multiple barrel cartridge assembly for storing separate materials in individual storage compartments, and a nozzle assembly containing a common mixing element for intermixing the materials fed through the mixing element from their respective storage compartments and a common spout for discharging the mixed product.
Various arrangements for removably coupling the nozzle assembly to the syringe are also described in the prior art. As long as the materials stored in the syringe are of relatively low viscosity so as to require minimal force to feed the materials through the common mixing element in the nozzle assembly, the particular coupling arrangement is of no consequence. However, for materials which are viscous and must be fed under pressure, the coupling arrangement becomes a limiting factor in the design of the dispenser. In the latter case, the removable coupling arrangement must be able to withstand the pressure required to feed the materials through the mixing element in the nozzle assembly, without the nozzle assembly separating from the syringe and without permitting leakage, particularly at the interlock. The coupling must also be inexpensive and simple enough to be readily uncoupled to permit reuse by replacement or substitution of another nozzle. If internal leakage occurs in the coupling area before discharging materials from the syringe into the nozzle assembly, the materials will polymerize and cross-contaminate at the orifice in the head of the syringe preventing use of the dispenser before the first usage. This is particularly important for any application in which the stored materials upon contact with one another form a polymerized product.
The design of the coupling arrangement to permit the nozzle to be removable from the syringe becomes a critical factor for intermixing and dispensing viscous materials due to the mechanical limitations of the device for a given size discharge orifice and to the back pressure created by the tortuous route which the viscous materials are forced, under pressure, to follow through the static mixing element in the discharge nozzle. Accordingly, the coupling between the orifice end of the syringe and the nozzle assembly must be secure enough to withstand the hydraulic pressure developed in the device to dispense the materials from the syringe through the nozzle assembly. It is equally important that the coupling not only interlock the syringe to the nozzle, but that it also form a pressure seal to prevent any leakage of material at the interlock.
The multiple barrel dispensing device of the present invention overcomes the shortcomings of prior art multiple barrel dispensing devices and permits a much wider range of viscous and/or non-viscous materials to be intermixed. The nozzle assembly is readily removed from the syringe permitting reuse of the dispenser by substitution of a new nozzle.